This invention is best described with reference to spot weld removal operations. The task of removing spot weld interconnections of upper and lower flat members is typically very time-consuming and difficult. Spot weld removing operations are regularly and frequently practiced in a variety of situations, most notably in vehicle panel replacement in auto body shops.
In removing a spot weld interconnection of upper and lower flat members, which are typically metal plates, it is usually highly desirable to remove the metal of the upper flat member at the location of a spot weld interconnection without removing any of the metal below the interface of the upper and lower flat members. Invasion of metal coincident with the lower flat member is undesirable. Removal of upper member metal alone is sufficient to disconnect the flat members, provided the metal removal is at the weld location.
Extremely careful tool manipulation and use is necessary to achieve removal of the upper flat member without invading the lower flat member. It is this which makes the operation difficult and time-consuming.
A variety of tools are used for spot weld removal. Bits of various kinds are frequently used, including drills, burr drills, end mills, and the like. Some of such bits have a working end which is substantially normal to the bit axis. This facilitates spot weld removal without invasion of the lower flat member, but the operation is still difficult and time-consuming.
Among other things, it is often difficult to control the depth of tool movement into the interconnected flat members. The lower flat member is usually invaded unless extreme care is taken in the operation. The operator often is required to guess the thickness (gauge) of the upper member, and even then is unable to properly limit the metal removal to metal above the interface.
And, with certain bit-like spot weld removing devices of the prior art, accurate placement of the tool over the spot weld portion is difficult. Furthermore, holding the tool at that portion during the spot weld removing operation, particularly at the beginning of the operation, is difficult.
Specialized tools have been developed to aid in removal of spot welded portions in sheet metal work. Among these are tools having annular cutting edges to cut an annular groove around a spot weld interconnection and a spring-loaded center guide pin to hold the tool in place during cutting of the annular groove. Another example is the specialized tool disclosed in U.S. Pat. No. 4,540,319 (Michiharu), which is a complex drilling device with apparatus to control the extent of the axial movement of a chuck having a drill mounted in it. Still other devices, to which bits may be secured, control the extent of axial movement by a bit for various purposes.
While such prior devices address some of the problems associated with removal of spot weld interconnections, there is a need for an improved spot weld removing device, of the type having a metal-removing bit directly attachable to a hand-held rotary drive, which will quickly, easily and accurately remove the spot weld portion of an upper flat member without invasion of the lower flat member. A tool allowing easy and more accurate placement on the proper spot is needed. A tool which may readily be adjusted to accommodate different thicknesses of the upper flat members to be removed is needed.
In summary, the devices of the prior art have not provided a simple, easily understood, easily usable and accurate spot weld portion removing device.